One proposed structure of the power output apparatus includes an internal combustion engine, two motors, a Ravigneaux planetary gear mechanism, and a parallel shaft-type transmission arranged to selectively connect two output elements of the planetary gear mechanism to an output shaft (see, for example, Patent Document 1). Another proposed structure of the power output apparatus has a planetary gear mechanism including an input element connected with an internal combustion engine and two output elements, and a parallel shaft-type transmission including a countershaft connected with the respective output elements of the planetary gear mechanism (see, for example, Patent Document 2). In the power output apparatus of this proposed structure, the two output elements of the planetary gear mechanism are respectively fixed to the inner circumferences of corresponding rotors in an electric driving system. A conventionally known structure of the power output apparatus has a power distribution mechanism including an input element connected with an internal combustion engine, a reactive force element connected with a first motor generator, and an output element connected with a second motor generator, and two clutches arranged to selectively connect an axle as an output member to the output element or the reactive force element of the power distribution mechanism (see, for example, Patent Document 3). In the power output apparatus of this conventional structure, when the first motor generator is rotated at a negative rotation speed to perform power operation, the two clutches are controlled to connect the reactive force element of the power distribution mechanism to the output member and disconnect the output element of the power distribution mechanism from the output member. Such control prevents the occurrence of power circulation where the first motor generator is driven with electric power generated by the second motor generator that uses part of the power of the output member.    Patent Document 1: Japanese Patent Laid-Open No. 2005-155891    Patent Document 2: Japanese Patent Laid-Open No. 2003-106389    Patent Document 3: Japanese Patent Laid-Open No. 2005-125876